River diversions retain microplastics’ presence on land

June 8, 2023
The new research confirms a link between urbanization, flow diversions, and microplastic transport in streams, finding that diversions can prevent microplastics from being transported to the ocean.

A new study finds that diverting streams and rivers to irrigate crops or provide drinking water may significantly extend the time that microplastics spend in river catchments before they flow into oceans.

The findings are shared in Water Research.

According to a press release by the University of Birmingham, an international group of scientists’ research highlights the impact of water management in terms of river diversions, for irrigation purposes, on microplastic transport.

These diversions can have significant impact on the estimates of the pollutant’s flow toward oceans, with the diverted water from rivers dispersing the tiny plastic particles across farmland from where they may be flushed back into other water courses or neighboring catchments.

The research team studied two paired rivers in Colorado — the Boulder Creek and its less urbanized tributary South Boulder Creek — evaluating the effects of urbanization and flow diversions on the up-to-downstream profiles of local microplastic concentrations as well as microplastic loads. This evaluation indicated the flow-weighted downstream transport of microplastic particles.

The researchers found that microplastic concentration patterns in both rivers were related to the degree of catchment urbanization: Data from both streams suggests a link between microplastic concentration and urbanization, as microplastic concentrations in Boulder Creek were higher in both surface water and sediment than in South Boulder Creek, and microplastic concentration increased in downstream direction when passing more urbanized areas.

“We discovered strong links between the degree of urbanization in the river catchment and observed river microplastic concentrations, highlighting how human activities resulted in immediate increase in microplastics in this mountainous catchment,” said lead author Anna Kukkola, from the University of Birmingham. “A key novelty of this study is the application of the loading approach which is used here for the first time for the quantification of microplastics fluxes and enabled us to not only identify microplastic sources but also determine the downstream evolution of microplastic transport patterns and in this case also the diversion of microplastics out of the river catchment.”

The international team also discovered that the magnitude of flow diversions from both streams resulted in large quantities of microplastic being removed from each stream and being transported out of their actual catchment. The team measured microplastic removal through flow diversions of over 500 microplastic particles per second (or 1,800,00 per hour) from the two rivers studied.

The researchers estimate that around 41 trillion microplastic particles are redistributed out of river networks into the terrestrial environment in North America every year, with as many as 459 trillion particles being redistributed globally.

While toxicity assessment was not a focus of the current study, co-author Professor Iseult Lynch from the University of Birmingham noted: “The results of this study are highly relevant for estimating ecotoxicological impacts on aquatic and terrestrial environments and ecosystems, with enhanced terrestrial residence times resulting in extended (chronic) exposures.”

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